As a method of driving a display apparatus, such as a CRT in a television set, deflection using a saw tooth wave is normally performed. In the case of, for example, horizontal scanning, a horizontal effective area is scanned at the leading edge of a saw tooth wave to display from the left end to the right end on a screen. On the other hand, the trailing edge becomes a retrace line interval for the horizontal scanning to return from the right end to the left end on the screen. At this time, video blanking is applied so that the scanning line, which returns, is not displayed. This horizontal retrace line interval is set to about 15% of the horizontal scanning interval.
In recent years, the screen of a television set tends to become larger, wide aspect displays have become widespread, and enlargement of the screen size has been proceeding. Demand for television sets with a small depth dimension (thin) in addition to a large screen is increasing.
The horizontal frequency of NTSC signals of an interlace scanning system is set to be 15.75 kHz. In contrast to that, the horizontal frequency of NTSC signals converted into a progressive scanning system (a line sequential system) is set to be 31.47 kHz. The use of this progressive scanning system has the advantage of being capable of reducing flickers of displayed pictures and providing images of high quality. Also, video signals having a higher horizontal scanning frequency than the conventional television signal are also increasing as in the case of highvision signals, PC signals and the like, and the horizontal deflection frequency tends to increasingly become a higher frequency.
Japanese Patent Laid-open Application No. Hei 3-76493 discloses a time axis compression apparatus for a television set for realizing such a progressive scanning system. In accordance therewith, it is possible to realize a progressive scanning system. Furthermore, this prior art makes it possible to compress the time axis of video signals in the horizontal period, and to show NTSC signals on a high definition display with their linearity maintained and without having to switch the horizontal deflection current. However, where NTSC signals are converted into a progressive scanning system, the horizontal frequency should be raised to about twice that of the interlace scanning system. Consequently, the current which flows to the horizontal deflecting coil of the deflecting yoke should also be approximately doubled, resulting in the problem of a power increase in the output section of the horizontal deflection circuit.
For this reason, a cost increase of the deflecting circuit, particularly the horizontal deflection circuit such as an increase in the power consumption of the horizontal deflection circuit and an expensive transistor being required has become a significant problem.